The present invention relates to an amplifier using common output terminals for dual modes of operation.
Certain integrated circuit (IC) chips have the ability to internally generate differential signals that are driven off chip. These differential signals take the form of the original differential signal or can be converted to a single ended signal. In order to provide the capability of either output, the IC chips use parallel output paths. One path drives the signal through a differential amplifier, maintaining the original form of the signal. The other path is used to transmit the differential pair to be driven off chip to an amplifier that converts it to a single ended signal. For configurations consisting of two differential signals, four pads on the IC chip are required, one pair of pads for the differential signal mode (both differential signals are identical) and two pads for the signals in the single ended mode. If the IC is required to function only in one mode at any given time, use of four pads can increase the complexity of the IC chip by consuming additional space for redundant pads that could otherwise be used for pads providing other output signals.
Accordingly, a need exists for a dual mode amplifier having a simplified output configuration.
A first amplifier having dual modes of operation includes two differential amplifiers each receiving a pair of differential input signals and having an output terminal. Circuitry couples the differential amplifiers together and is controlled by a control signal. A first value of the control signal activates the circuitry so that the differential amplifiers can provide a differential signal at the output terminals in response to the differential input signals. A second value of the control signal deactivates the circuitry so that the differential amplifiers can operate independently to provide a pair of single ended signals at the output terminals in response to two differential input signals.
A second amplifier having dual modes of operation also includes two differential amplifiers each receiving a pair of differential input signals and having an output terminal. The second amplifier includes coupling circuits, controlled by a control signal, for coupling together corresponding differential input signals. A first value of the control signal activates the coupling circuits so that the differential amplifiers provide a differential signal at the output terminals in response to the differential input signals. A second value of the control signal deactivates the coupling circuits so that the differential amplifiers operate independently to provide a pair of single ended signals at the output terminals in response to two differential input signals.
These exemplary first and second amplifiers can also be used to implement a method for providing dual modes of operation in an amplifier using only one set of output terminals.